This invention pertains to the field of liquid crystal display (LCD) devices, such as liquid crystal on silicon (LCOS) devices, and more particularly to light shielding in such devices.
Reflective LCD devices are well known. Examples of such devices, and in particular active matrix devices, are shown in U.S. Pat. Nos. 6,023,309 and 6,052,165. With reference to the following description, familiarity with conventional features of such devices will be assumed, so that only features bearing on the present invention will be described.
FIG. 1 shows a portion of typical prior-art reflective LCD device 100. The reflective LCD device 100 may generally be divided into a pixel region 100a (active region) and a peripheral region 100b. The pixel region 100a includes an array of pixel elements and the peripheral region 100b includes driver circuits 105 for supplying driving signals to each of the pixel elements.
The LCD device 100 comprises, in relevant part, a silicon substrate 110, an insulating layer 112, a liquid crystal layer 114, a transparent electrode 116, such as indium-tin-oxide (ITO), and a glass layer 118. A reflective mirror (pixel) metal layer 120 is provided beneath the liquid crystal layer 114 on the insulating layer 112. The mirror metal layer 120 includes a plurality of individual reflective pixel electrodes 120a in the pixel region 100a, with light transmissive regions 122 being located between the pixel electrodes 120a. 
Also provided in the insulating layer 112 and between the mirror metal layer 120 and the substrate 110 are at least three metal layers 124, 128 and 130. In the pixel region 100a, the metal layers 128 and 130 form mutually-orthogonal row and column lines, which may be connected to gate and source electrodes of MOS transistors (not shown in FIG. 1) for pixel elements fabricated in the underlying substrate 110. In the peripheral region 100b, the metal layers 128 and 130 form signal routing lines used for routing various signals of the driver circuits 105. Also, metal plugs or vias 132 are provided for connecting various portions of first, second, third and fourth metal layers 120, 124, 128, 130 with each other.
In addition, the metal layer 124 is provided to prevent light entering the device, such as through the transmissive regions 122 between the pixel electrodes 120a, from reaching the substrate 110 where it might induce leakage currents or otherwise interfere with proper device operation. Note that while portions of metal layers 128 or 130 may incidentally block a small portion of light entering the device, the structure of FIG. 1 requires a separate metal layer 124 to be dedicated to provide the required degree of light blocking in the peripheral region 100b. This is due to the fact that light trapped between the two metal layers 120 and 124 can propagate over long distances due to multiple reflections between the layers.
While this prior-art solution is satisfactory for blocking light from reaching the substrate 110 in the peripheral region 100b, it requires the additional dedicated metal layer 124 in the peripheral region 100b. However, the area required for the driver circuits 105 could be reduced if the metal layer 124 could also be used for routing driver circuitry signals in the peripheral region 100b, instead of being dedicated only to light blocking.
Accordingly, it would be desirable to accomplish the light-blocking function of the dedicated metal layer in the peripheral region of the prior art devices without using a separate dedicated metal layer in this region. Other and further objects and advantages will appear hereinafter.
Therefore, in one aspect, the invention provides a liquid crystal display (LCD) which blocks light in the peripheral driver circuit region of the device without providing a dedicated metal layer in this region for this purpose.
Accordingly, an LCD device is provided having a pixel region and a peripheral region adjacent to the pixel region, comprising a substrate, a first metal layer above the substrate including an array of pixel electrodes in the pixel region and a peripheral portion in the peripheral region, a second metal layer beneath the array of pixel electrodes, and a wall disposed between the second and first metal layers along an edge of the pixel region and extending upward to the peripheral portion of the first metal layer.